MEDUSA OF MICROHYDRA RYDEEf. 637 



well expanded, but there are indications of four small lips, 

 which are simply infolds of the margin. 



Canal system. — There are four radial canals, which are 

 not at all conspicuous, and have the appearance of thin lines 

 running from the base of the stomach to the margin of the 

 umbrella. In fact the canals are rendered visible by the 

 brownish colouration of their endoderm cells. A circular 

 canal is probably present, but the thick layer of ectoderm 

 round the margin of the umbrella prevented me from finding 

 a definite canal. To demonstrate the existence of a circular 

 canal would have necessitated the cutting of sections. 



Absence of gonads. — The specimen does not show the 

 slightest trace of gonads. The figures of the Medusa illus- 

 trating Potts' paper (PI. 36, figs. 13 and 14) would lead one 

 to believe that gonads were present along the whole length of 

 the radial canals and that they also extended round the 

 stomach. The Hydromeduste either have their gonads upon 

 the stomach and its lobes, or else upon the radial canals, but 

 none are known to possess gonads in both positions. If a 

 Medusa was found with gonads upon the stomach and radial 

 canals it would have to be placed in a special order. These 

 shaded thickenings are undoubtedly misleading, and I fail to 

 see what they are intended to represent. 



Tentacles (PI. 37, fig. 2). — There are eight tentacles (four 

 per-radial and four inter-radial) similar in size and shape. 

 They are probably in a semi-contracted condition, which gives 

 them a rather stunted appearance. The base of the tentacles 

 is apparently attached for a very short distance, on its upper 

 side, to the margin of the umbrella. The manner in wdiich 

 the tentacles curl at their base and hang down points to an 

 attachment, though I could not clearly see it. There is no 

 indication of a definite basal bulb at the base of the tentacles. 

 Neraatocysts are very scarce in the tentacles, and it was only 

 after a long search that I found any, as they were not on the 

 surface but underneath the ectoderm cells. 



Around the margin of the umbrella there is a thick layer 

 of ectoderm cells, similar in structure to those of the tentacles, 



